ARLINGTON, Va. – Needed to keep a school building running these days: Water, electricity – and broadband.

Interactive digital learning on laptops and tablets is replacing traditional textbooks in many cases. Students are taking computer-based tests instead of fill-in-the bubble exams. Teachers are accessing far-off resources for lessons.

Technology is changing the way students are taught – and tested. But there's a catch – most of it is occurring in schools that have rich connectivity to the Internet.

Although nearly every school has Internet access, classrooms frequently are not connected or the connections are super slow.

The hurdle is limited capacity inside schools to transmit data, or bandwidth.

"It's the backbone. We have to actually think not just about the sustainability of the current traffic, we're talking about exploding traffic," said Raj Adusumilli, assistant superintendent for information services in the Arlington Public Schools in northern Virginia.

The effort to get high-speed Internet access in every school got a boost Wednesday from the philanthropy of two technology gurus – Facebook creator Mark Zuckerberg and Microsoft Corp. co-founder Bill Gates. Zuckerberg's Startup: Education and Gates' foundation have contributed a combined $9 million to the nonprofit EducationSuperHighway, a San Francisco-based nonprofit working to improve connectivity in schools.

"When schools and teachers have access to reliable Internet connections, students can discover new skills and ideas beyond the classroom," Zuckerberg said in a statement.

The funds are expected to be used to provide technical expertise to schools and use competition to help drive costs down.

It likely would cost billions to get high-speed Internet access to every school in America.

President Barack Obama this past summer set a goal of having 99 percent of students connected to high-speed Internet connections within five years. Also, the Federal Communications Commission is weighing changes to a program to increase connectivity in schools.

Today, about 80 percent of schools have Internet capabilities that are too slow or isolated to places like front offices and computer labs, said Richard Culatta, director of education technology at the Education Department. Many schools have the same amount of connectivity as an average home. That means several hundred kids or more operate on an Internet connection similar to that used in a house by four family members. That leads to networks that are slow and prone to crashing.

"There are many examples of fantastic things happening across the country, but they are happening in places where infrastructure is in place that supports these types of innovations," Culatta said.

At Jamestown Elementary School in Arlington, Va., first and second graders use iPads to document the growth of caterpillars for a science project or record themselves reading out loud as they make electronic books.

"It's fun. You can draw and make books and movies," said 7-year-old Braeden Meeker. "We learn writing and math. We learn a lot of things."

But one day in class, the system crashed when students tried to look up their house on a Google map.

The district has upgraded to high-speed broadband, or Internet access that is always available and faster than dialup, in middle and high schools and is in the process of doing the same in elementary schools. The district's goal is to assign a device to each student by 2017.

In some districts, particularly rural ones, cost is a huge factor in getting access to lines that would bring broadband into schools. To buy the equipment and install Wi-Fi costs an estimated $30,000 to $50,000 per school and to run fiberoptics into the school can cost tens of thousands more per mile, said Evan Marwell, CEO of EducationSuperHighway.

A lack of competition for broadband access helps drive up costs at Chautauqua County Unified Schools, a district with about 360 students in an agriculture and oil community in rural Kansas. About three-quarters of students in the district qualify for free or reduced lunches.

The district relies on distance learning to teach Spanish, physics and calculus and has issued an iPad to all students in upper grades, said Nancy Pinard, the district's technology director. Its broadband bill would be about $9,000 a month without a special Federal Communications Commission program that reduces it to $2,000 to $3,000 a month.

"My big thing is the cost of it," Pinard said. "How long will be able to maintain where we are at just because of the cost."

The drive for increased broadband capabilities has been fueled in part by a drop in the price of tablets and their rising popularity, said Doug Levin, executive director of the State Educational Technology Directors Association. More apps and other educational software are available and states and districts have loosened rules to allow textbook dollars to be spent on digital learning, he said.

"It used to be OK that some students could access these opportunities and others couldn't, and the big shift is now there really is an expectation that all kids need to access" these opportunities, Levin said.

Another factor is preparation for tests connected to Common Core academic standards rolling out in most of the country. The shift to computer-based tests requires more bandwidth than many districts have.

Randi Weingarten, president of the American Federation of Teachers, said the issue goes beyond technology in schools. About half of American children live in poverty and many of them don't have technology at home, she said.

At the same time, she questioned Zuckerberg's and Gates' motives. "So the question I have is, why are these foundations doing this now? Are they doing it because of the Common Core testing? Or, are they doing it because we want to actually help kids succeed," Weingarten said in an interview.

A few minutes later, she amended her response. "Let me just say on the record, it's great that they want to help deal with the digital divide. I'd like for them to help with other things as well but it's great that they want to help with the divide."